Envelope detector, linearization circuit, amplifier circuit, method for detecting a modulation envelope and wireless communication unit

ABSTRACT

An envelope ( 100 ) detector for detecting a modulation envelope of a modulated signal. The envelope detector includes a sensor ( 102 ). The sensor has a sensor input ( 1021 ), for sensing a signal forming a measure for the amount of electrical power presented at the sensor input ( 1021 ). The sensor input ( 1021 ) is electrically conducting connectable to an electrical path ( 14 ), along which electrical path ( 14 ) the modulated signal is transmitted. The detector ( 100 ) includes a filter ( 103 ) for removing from the sensed signal a part contributed to non-envelope signal components in the modulated signal; and a detector output ( 104 ) connected to the filter ( 103 ) for outputting an envelope signal.

FIELD OF THE INVENTION

This invention relates to, an envelope detector, an amplifier circuit, awireless communication unit and a method for detecting a modulationenvelope.

BACKGROUND OF THE INVENTION

Amplifiers are generally known in the art. For example, power amplifiersare widely used in wireless transmission systems to amplify a signalsuch that the signal has sufficient energy to be transmitted via anantenna. However, often the performance is limited by the non-linearbehaviour of the Power Amplifier (PA). To obviate the non-linearbehaviour of the PA, various techniques are known, such as predistortionand envelope injection techniques.

For example Chi-Shuen et al. “A New Approach to Amplifier Linearizationby the Generalized Baseband Signal Injection Method”, IEEE Microwave andWireless Components Letters, VOL. 12, N^(o) 9, pp 336-338. September1999 discloses a circuit which determines a base-band signal from aninput signal, and injects the base-band signal into a power amplifier.The circuit further injects the base-band signal into a diodepredistorter, which is connected to the amplifier as well. The circuitincludes a coupler by means of which a combined capacitive and inductiveconnection to a signal path is established, in order to receive theinput signal. The coupler is connected to the gate of a MESFET, whichacts as a low frequency detector. The output of the MESFET istransmitted to respective operational amplifiers (opamps). Each of theopamps provides an amplified signal to a corresponding quarterwavelength phase-shifter. The quarter wavelength phase shifters areconnected to the diode predistorter and the amplifier, respectively.

However, a disadvantage of this circuit is that it consumes asignificant amount of power and leads to a trade off between linearityand power added efficiency (PAE). Furthermore, it is difficult toimplement as an integrated circuit, because the operational amplifiersare typically manufactured with a different kind of process than thepower amplifier. Also, the circuit has a large footprint because thecoupler occupies a large amount of space.

SUMMARY OF THE INVENTION

The present invention provides an envelope detector, a linearizationcircuit, an amplifier circuit, a wireless communication unit and amethod for detecting a modulation envelope as described in theaccompanying claims.

Specific embodiments of the invention are set forth in the dependentclaims.

These and other aspects of the invention will be apparent from andelucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details, aspects and embodiments of the invention will bedescribed, by way of example only, with reference to the drawings.

FIG. 1 shows a block diagram of a first example of an embodiment of anamplifier circuit

FIG. 2 shows a block diagram of a second example of an embodiment of anamplifier circuit.

FIG. 3| shows a block diagram of an example of an embodiment of awireless communication unit.

FIGS. 4-XX show graphs of simulated amplitudes as a function of time atdifferent nodes in the example of FIG. 2

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Although in the following an example of an embodiment will be describedwhich forms an amplifier circuit, it should be noted that the inventionmay be implemented in any other type of electronic circuit and theinvention is not limited to applications in amplifier circuits.Referring to FIG. 1, as shown therein by way of example, an amplifiercircuit 1 may include a power amplifier (PA) 10 with one or moreamplifier stages 11-12 and may include one or more preceding stages 13positioned upstream of the power amplifier 10. The amplifier circuit 1further may include a bias source 140 and a linearization circuit orlinearizer 16. The amplifier circuit 1 may process a modulated signaland, for example output a modulated signal via an electrical path 14.

The linearizer 16 may, as shown in FIG. 1, include an envelope detector100. The envelope detector 100 can detect a modulation envelope of themodulated signal and output an envelope signal which represents themodulation envelope. The envelope detector 100 may, as shown in FIG. 1,for instance include a detector input 101, a power sensor (SNS) 102, afilter 103, and a detector output 104. As shown in the example of FIG.1, the sensor 102 may include a sensor input 1021 and a sensor output1022. The sensor input 1021 may be connected to the envelope detectorinput 101. The sensor output 1022 of the sensor 102 may be connected toa filter input 1031. The filter 103 may be connected with a filteroutput 1032 to the envelope detector output 104.

The envelope detector 100 may operate as follows. The sensor 102 maysense a parameter which forms a measure for the amount of electricalpower presented at the sensor input 1021. The sensor 102 may for examplesense the current transmitted along an electrical path 14 to which thesensor input 101 is connected via an electrically conducting connection.As for instance shown in the example of FIG. 1, the sensor input 1021 isconnected via an electrically conducting connection to a node 15 of anelectrical path 14 along which a modulated signal may be transmitted.The sensor 102 may output a signal representing the sensed parameter tothe filter 103. The filter 103 may remove a part of the frequencycomponents present in the sensed signal, resulting in an envelopesignal. The part may for example be at least a part of the componentswith frequencies different from the frequencies of the signal envelope.The filter 103 may subsequently output at the envelope detector output104 the envelope signal.

As shown in the example of FIG. 1, the envelope detector 100 does nothave a coupler. Accordingly, the footprint of the envelope detector 100may be reduced, and implementation of the envelope detector 100 in anintegrated circuit may be less complex. Also, the envelope detector 100may be implemented without operational amplifiers, and hence beimplemented in the same integrated circuit as, for example, theamplifier 10.

The sensor 102 may be implemented in any manner suitable for thespecific implementation. The sensor 102 may generate, from the inputtedsignal, a signal which can be inputted in the filter 103 and whichincludes information about the envelope of the modulated signal.

The sensor 102 may for example include a current sensor for sensing theamount of current flowing through the electrical path 14. The amplifiermay have for example a current output. Without wishing to be bound toany theory, since for a current output the voltage at the current outputis constant, e.g. determined by the power source Vs of the amplifier,the current forms a measure for the outputted amount of power. To sensethe current, the sensor 102 may for example be connected with the sensorinput 1021 to a node 15 of the electrical path 14, and a part of theelectrical power flowing through the electrical path 14 may be fed tothe sensor 102 via the sensor input 1021. Referring to the example shownin FIG. 2, the envelope detector 100 may for example include anelectrical conducting path 1023 between the node 15 and the sensor 102.An image signal, for instance an image current, may be fed into thesensor 102 via the electrical conducting path 1023.

For instance, in the example of FIG. 2, the sensor 102 includes anactive electrical device T2 which generates a current signal which is animage of the power amplifier output signal. That is, the current signalhas substantially the same frequency characteristics as the signalsensed at the sensor input 1021, i.e. as the modulated signal. However,the current signal may for example differ in amplitude compared to themodulated signal. The current signal may be very small compared to themodulated signal. For example, the current signal may have a currentamplitude which is less than 1% of the amplitude of the modulatedsignal, for example 0.25% or less, such as 0.1% or less. For instance, aratio of the power of the current signal relative to the power of themodulated signal which allows an accurate determination of the envelopesignal without significant changes in the output of the amplifier isfound to be 0.01 dB or less.

The active electrical device T2 be any suitable type of device. Theactive electrical device may for example include an controllable currentsource which is connected with a current input to the electrical path14, such as a bipolar transistor (BT) such as a Heterojunction BipolarTransistor (HBT), a field effect transistor or other controllablecurrent source. The active electric device may for example be of a typesimilar to an active device which outputs the modulated signal. Forexample, as shown in FIG. 2, the active electric device may be atransistor in case the active device is a transistor and be the sametype of transistor as the device that outputs the modulated signal, e.g.in the example of FIG. 2, the PA transistor 11.

As shown in FIG. 2, an electrically conducting path 1023 may be presentbetween a device terminal Cl2 of the active electrical device T2 and theelectrical path 14. Via the device terminal Cl2, the active device T2may draw a part of the current into the sensor 102, which part isproportional to the current flowing through the electrical path 14. Theactive electrical device T2 may have another device terminal foroutputting the current signal. As shown in FIG. 2, the active device T2may for instance output the current signal at a current output Em2. Thecurrent output Em2 may, for example, be directly connected to a filterinput 1031 of the filter 103. However, the output may also be connectedindirectly to the filter input 1031. The sensor 102 for instance mayinclude a current-to-voltage converter R4 which connects the currentoutput Em2 to the filter input 1031 and converts the current into avoltage in order to input the voltage into a device downstream of thecurrent-to-voltage converter, e.g. into a voltage filter 103 whichremoves from a voltage signal components of undesired frequencies.

The sensor 102 may include a current control input 106 at which a signalmay be presented which controls the current drawn by the active devicesource. As for instance shown in the example of FIG. 2, the activeelectrical device T2 may have an amplitude control input Bs2 at which anamplitude control signal may be inputted. The current control input 106may be connected to the amplitude control input Bs2, which in theexample of FIG. 2 is formed by a base of the HBT.

The amplitude control signal may for example be the same signal as aninput signal presented to a device to which the modulated signal ispresented or by which the modulated signal is outputted. As is explainedbelow in more detail, for example, the amplitude control signal may be amodulated signal inputted to an amplifier 10, or other device, to whichthe envelope signal is inputted, be processed, e.g. amplified, togetherwith the modulated signal. Thereby, the modulation distortion incurredin the electronic device due to non-linear behaviour can be reduced.

The active electrical device T2 may be arranged to control at least theamplitude of the current signal based on the amplitude control signal.In case, as for instance shown in FIG. 2, the active electrical deviceincludes a transistor, such as a BT, a HBT for example, the currentflowing through the transistor, e.g. from the collector of the BT to theemitter, is proportional to the voltage applied at the amplifier controlinput, e.g. at the base of the BT. The transistor, e.g. the BT in FIG.2, may for example be operated in the linear region and output a currentat the emitter which is linearly dependent on the voltage provided atthe base.

As shown in FIG. 2, the active electrical device T2 may have a biasinput connected to a sensor bias input 105. At the bias input, a biassignal may be inputted. The bias signal may for example be the same biassignal as the bias signal presented to a device to which the modulatedsignal is presented or by which the modulated signal is outputted. Asfor instance shown in the example of FIG. 2, the active electricaldevice T2 may include a BT, a HBT for example, which is connected withits base to the sensor bias control input 105.

The sensor 102 may as shown in FIG. 2 include a voltage output 1022 foroutputting a voltage proportional to the sensed amount of current. Togenerate this voltage, the sensor 102 may for example include acurrent-to-voltage converter R4 which converts the amount of currentflowing through the active device T2 into a voltage. The converter R4may convert the current signal into a voltage signal and input thevoltage signal into the filter 103. In the example of FIG. 2, forinstance, the sensor 102 includes a current path between the sensorinput 101 and a current-to-voltage converter R4. Via the current path, acurrent signal representing the signal sensed at the sensor input 1021may be sent to the converter R4. The current-to-voltage converter R4may, as shown in FIG. 2, consist of a single resistor, however, thecurrent-to-voltage converter R4 may be implemented with more components.In the example of FIG. 2, the resistor R4 connects the active device T2to ground GND or other reference voltage. Since the voltage over theresistor R4 is proportional to the current flowing through the resistorR4, the current signal can be converted into a voltage signal.

The envelope detector 100 may consist of passive components andtransistors only. Thereby, the envelope detector 100 may be especiallysuited for implementation in a single integrated circuit. Furthermore,the components of the envelope detector 100 may be manufactured in thesame process as an amplifier, and accordingly may thereby be implementedin the same integrated circuit as the amplifier 10. As for example shownin FIG. 2, the envelope detector 100 may consist of transistors,resistors and capacitors only.

Between sensor input 1021 and the active device T2, a power limiter maybe present. The power limiter may limit the amount of power inputted tothe sensor 102, to prevent a power overload of the components in thesensor 102. For example, in case the sensor 102 includes an activedevice T2, operation of the active device T2 in a desired region may beensured. For example, in case the active device T2 includes a BT, suchas a HBT, the collector current Ic may degrade when the amount of powertransmitted over the electrical path 14, and hence the sensed signal,exceeds a threshold. For example, without wishing to be bound to anytheory, it has been found that at a Power Amplifier output power of 15dBm or more the collector current of a HBT might deteriorate due to thenegative swing of the collector current.

The power limiter may for example an RC network between the sensor 102and the detector input 101. For instance in the example of FIG. 2, aresistor R3 connects an input Cl2 to the envelope detector input 101. Acapacitor C3 connects a node between the resistor R3 and the activedevice T2 to ground. The RC network reduces the RF swing and especiallythe negative swing at the part indicated with reference sign 1023 inFIG. 2. The RC circuit may have a time-constant τ which is smaller thanthe inverse of the carrier frequency f_(carrier), that isτ<1/f_(carrier). The resistor R3 may for example have an impedance whichis (much) higher than the output impedance downstream of the path 14 inorder to minimize the leakage of power via the envelope detector 100.

The envelope detector 100 may include a phase shifter for shifting thephase of the envelope signal relative to the modulated signal. Theenvelope detector 100 may include a phase shifter 107 The phase shifter107 may, for example, shift the phase of the sensed signal or theenvelope modulation signal, for example to have the envelope modulationsignal match phase requirements imposed by the application of theenvelope detector 100. For instance, as explained below in more detailthe envelope detector may be used to reduce inter modulation distortion(IMD) by injecting the envelope signal into a device which processes themodulated signal, and the phase shifter may adjust the phase of therespective signal to ensure that the injected envelope signal has aphase which reduces the distortion components in the signal.

The phase shifter may be implemented in any manner suitable for thespecific implementation. In the example of FIG. 2, for instance, thephase shifter 107 may for example include the filter 103 and/or the RCnetwork R3/C3 and/or the capacitance present in the active device T2.The phase shifter 107 may be present between the sensor input 1021 andthe filter output 1032. The phase shifter may be included in componentsof the envelope detector performing other functions as well, such as inthe example of FIG. 2, in the filter, the RC circuit or the activedevice T2. Thereby a reduction of the number of components in thecircuit is enabled.

The filter 103 may be implemented in any manner suitable for thespecific implementation. The filter may be connected with a filter input1031 to the sensor 102, to receive the sensed signal. The filter 103 mayremove from the sensed signal undesired signal components, and more inparticular remove RF frequency components not included in the modulationenvelope of the signal. The filter 103 may for instance removecomponents such as the carrier or other non-envelope components such asintermodulation products from the sensed signal. The filter 103 may forexample include a low-pass filter. The filter 103 may for example be anactive filter or be a passive filter, such as a LC filter or, as forinstance in the example of FIG. 2, an RC filter. The filter 103 may forexample be a first-order filter, a second order filter or a higher orderfilter.

The passive, low-pass filter may for example include a series RC-circuitwhich low-pass filters a voltage signal presented at a filter input1031. The low-pass filter may have a cut-off frequency below the carrierfrequency of the modulated signal and above the frequency f_(env) of themodulation envelope. For example, without wishing to be bound to anytheory the low-pass filter is found to effectively function withf_(env)<f_(cut-off)<N·f_(env) and N being equal or larger than 3. Forexample, the cut-off frequency may be equal or larger than 200 KHz, suchas 1.1 MHz or more, for example 4 MHz or more. the cut-off frequency maybe lower than 2 GHz, such as lower than 800 KHz for example. As shown inFIG. 2, the filter may be connected with a filter output 1032 to thedetector output 104. The filtered signal may be outputted via the filteroutput 1032 to the detector output 104 and be presented to anotherdevice, e.g. a bias source 140.

The envelope detector 100 may output the modulation envelope signal atan output 104 to other device. The output 104 may be connected to acapacitor C6 which reduces the DC level of the signal provided to theoutput 104. For example, the capacitor C6 may remove the DC off-setcaused by the filter 103 such that the signal presented at the output104 has a DC level of about zero.

The envelope detector 100 may be provided in any suitable device, forexample in a demodulator or other suitable device. As shown in FIGS. 1and 2, the envelope detector 100 may for example be present in a device,e.g. a power amplifier, and be connected with the detector output 104 toa node in the signal path of the device. The detector 100 may feed theenvelope signal to the node and cause the generation of intermodulationproducts (IMD) components that at least partially cancel the inherentIMD components that are produced by the device due to the device inputsignal and the inherent non-linearity of the device. Thereby theout-of-band emissions may be reduced. The IMD components caused by theenvelope signal may for example be in anti-phase (out of phase) with theinherent IMD components of the amplifier. The IMD components caused bythe envelope signal may for example have substantially the samemagnitude as the inherent IMD components.

As shown in FIGS. 1 and 2, the envelope detector 100 may for example beconnected to a bias source 140 and feed, for example, the envelopesignal into the bias source 140. The bias source 140 may be connected toa device to which the bias source provides a bias signal. Thereby, forexample, a bias signal can be generated which causes a device togenerate an intermodulation distortion reducing signal that at leastpartially reduces the inherent intermodulation distortion components ofthe electronic device, e.g. the power amplifier (PA). The electronicdevice may for example be an active device such as a Low Noise Amplifier(LNA), a mixer, a down converter, an up converters or a frequencymultipliers.

In the example of FIG. 1, the envelope detector is connected to a biassource which provides a bias to the output stage 11. However, theenvelope signal may in addition, or alternatively, be inputted at otherpositions in the amplifier circuit 10, for example in a stage 12,13upstream of the output stage 11 to cause the amplifier circuit togenerate signal components that at least partially cancel inherentdistortion components generated in the circuit. Thereby, the linearityof the amplifier circuit may be improved.

The device may for example be an amplifier 10. The amplifier 10 may beany suitable type of amplifier. The amplifier 10 may for example be apower amplifier, such as an RF power amplifier. As shown in the exampleof FIG. 1, the amplifier 10 may have one or more amplifier stages 11,12.The amplifier stages 11,12 may have an amplifier stage input, and one ormore amplifier stage outputs. For instance, the amplifier 10 may have aninput stage 12 which drives a stage downstream of the input stage, suchas an output stage 11. The input stage 12 may for example include adifferential amplifier stage. As shown in FIG. 1, the amplifier circuit1 may include one or more preceding stages 13, which are positionedupstream of the actual amplifier 10. The preceding stages 13 may forexample a pre-distortion stage or other suitable type of stage. In theexample of FIG. 1, an input 131 of the most upstream stage 13 isconnected to an input RFin of the amplifier circuit 1. An output 132 ofthe most upstream stage 13 is connected to a stage input 121 of anamplifier input stage 12 which is positioned, in a signal processingdirection, downstream of the most upstream stage 13. The stage output122 of the stage 12 may for example be connected to other stagesdownstream thereof. As shown in FIG. 1, an output stage 11 is connectedwith a stage input 111 to one or more of the amplifier stages upstreamof the output stage and is connected with a stage output 112 to anoutput RFout of the amplifier circuit 1. As shown in the example of FIG.2, another terminal 114 of the output stage 11 may be connected toground GND.

The envelope detector 100 may for instance be present in a feedforwardloop or in a feedback loop. As shown in FIGS. 1 and 2, the envelopedetector 100 may for example be present in a feedback loop 20 whichconnects the output of an electrical device to a signal input or a biasinput. For instance, in the examples of FIGS. 1 and 2, the envelopedetector 100 is part of a feedback loop 20 of an amplifier 10. Thefeedback loop 20 may connect e.g. the amplifier output RFout to theamplifier input RFin or one or more of the preceding stages 11-13.However, the feedback loop 20 may alternatively or in addition, as shownin FIGS. 1 and 2, connect the output of the amplifier 10 to a bias input113.

As shown in FIGS. 1 and 2, the feedback loop 20 may include the envelopedetector 100. Thereby, for example the envelope of the signal outputtedby the amplifier 10 can be fed back, for example to at least partiallyreduce inter-modulation distortion and for example suppress undesiredinter-modulation components generated in the amplifier 10. In thisrespect, it should be noted that inter-modulation distortion generallyrefers to a multi-frequency distortion product that results when (a)modulated signal(s) with two or more different carrier frequencies arepresented at the input of a non-linear device. All electronic devicesinherently exhibit a certain degree of non-linearity, even those whichare biased for “linear” operation. The spurious products which aregenerated due to the non-linearity of a device are mathematicallyrelated to the original input signals. For sake of simplicity, in thefollowing the input signal contains two frequencies. However it will beapparent that the input signal may include three or more frequencies.For an input signal including two frequencies f1 and f2, the frequenciesof the output signal, including the inter-modulation products, can becomputed by the equation:

f _(M,N) =M·f1±N·f2, where M, N=0, 1, 2, 3, . . .   (1)

With f_(M,N) representing the frequency. The order of the distortionproduct is given by the sum of M and N. Accordingly, the second-orderinter-modulation products of two signals at f1 and f2 would occur for{M=1, N=−1}, {M=−1, N=1}, and hence at f1−f2 and f2−f1. In this respect,it should be noted that the harmonic components of the input signals f1and f2, such as 2·f1, 2·f2, 3·f1, 3·f2, etc. are not considered asintermodulation products.

Third order inter-modulation products of the two signals, f1 and f2,would be at frequencies: 2·f1+f2, 2·f1−f2, f1+2·f2, f1−2·f2. Where 2·f1is the second harmonic of the signal at frequency f1 and 2·f2 is thesecond harmonic of the signal at frequency f2. Of these frequencies,only the frequencies 2·f1−f2 and 2·f2−f1 are commonly referred to as thethird order inter-modulation (IMD3) products, since typically thefrequencies 2·f1+f2 and f1+2·f2 are outside the carrier band. Forexample, for most types of modulated signals, such as amplitudemodulated signals, frequency modulated signals, phase modulated signals,the spectrum of the modulated signal includes frequencies f1 and f2which are related to each other by f1=f_(carrier)−f_(env) andf2=f_(carrier)−f_(env) where f_(env) is the envelope frequency.Typically the carrier frequency f_(carrier) is (much) larger than theenvelope frequency f_(env). Accordingly, f1 and f2 are relatively closeto each other, and the third order terms 2·f1−f2 and 2·f2−f1 will beclose to f1 and f2 as well. Accordingly, a regular band-pass filter willnot remove the IMD3 since the IMD3 components are within the pass-bandof the filter. To reduce the third order modulation, the envelope of thesignal can be injected into the, non-linear, electronic device, withsuitable amplitude and phase shift relative to the phase of theinter-modulation product to be reduced.

In the example of FIG. 1, the output of the amplifier 10 is connected bythe feedback loop 20 to a bias input of the output stage 11 of theamplifier 10. In the feedback loop 20 the envelope detector 100 may, asshown in FIG. 1 or 2, be connected with the envelope detector output 104to a bias control input 141 of a bias source 140. The bias source 140 isconnected with a bias output to a bias input 113 of the amplifier 10. Inthe example of FIG. 1, for instance, the bias input 113 is connected tothe output stage of the amplifier 10 and is able to provide a biasvoltage (or current) to the output stage 11. The bias voltage (orcurrent) may hence be at least partially controlled by the signalinputted at the bias control input 141. The bias source 140 may forexample include a DC bias source which provides a constant bias and avariable bias source which is connected to the bias control input 141which provides a variable bias which is superimposed on the DC bias. Thebias may for example be a voltage/current bias, and as shown in FIG. 2,a ballasting resistor R1 may be present between the bias output 142 andthe bias input 13 of the amplifier 10, in order to ensure thermalstability of the amplifier 10.

The envelope detector 100 may for example be connected with the input1021 of the sensor 102 to the electrical path 14 downstream of theamplifier output RFout. The envelope detector output 104 may for examplebe directly or indirectly connected to an input of the amplifier outputstage 11. The amplifier circuit may for instance include a bias source140 connected to a bias input 113 of a respective stage 11-13 of theamplifier circuit 1. The bias source 140 may, as shown in FIG. 1 have abias control input 141. At the bias control input 141 a bias controlsignal may be inputted which controls the amount of bias provided by thebias source 140. The bias control input 141 may for example be connectedto the envelope detector output 104, and accordingly the bias may becontrolled based on the envelope signal.

The amplifier circuit 1 may be used in any suitable type of device orapparatus. For instance, the amplifier 10 may be used in a wirelesscommunication unit, for example to amplify a RF signal to an amplifiersignal suitable to be transmitted by an antenna over a wirelessconnection. The wireless communication unit may for example include asignal generator, an amplifier circuit 1 and an antenna. The signalgenerator may generate a signal and transmit the generated signal to theamplifier 10. The amplifier 10 may amplify the generated signal suchthat the signal contains a sufficient amount of energy to be convertedinto an electromagnetic wave via the antenna and transmit the amplifiedsignal to the antenna.

For instance, FIG. 3 shows a block diagram of an example of anembodiment of a wireless communication unit 200 which includes anamplifier circuit 1. The wireless communication unit 200 may comprise anantenna 201, which may for instance be connected to a duplex filterduplexer or an antenna switch 202 that provides isolation between areceiver chain 221 and a transmitter chain 220 within the wirelesscommunication unit 200. The receiver chain 221 may include a receiverfront-end circuit 203. The receiver front-end circuit 203 may forexample provide a reception and/or filtering and/or intermediate orbase-band frequency conversion. The receiver front-end circuit 203 maybe connected, in this example via a serial coupling, to a signalprocessor 208, which may be implemented as a digital signal processor(DSP). An output from the signal processor 208 is provided to a suitableuser interface 209, which preferably comprises an output device 211,such as a speaker and/or display, and an input device 210, such as amicrophone and/or keypad.

The user interface 209 may be connected to a memory unit 206 and a timer204, for instance via the signal processor 208 and/or a controller 205.The controller 205 may also connected to the receiver front-end circuit203 and the signal processor 208. The controller 205 may for examplereceive bit error rate (BER) or frame error rate (FER) data fromrecovered information. The controller 205 is connected to the memorydevice 206 for storing operating regimes, such as decoding/encodingfunctions and the like. A timer 204 may be connected to the controller205 to control the timing of operations (transmission or reception oftime-dependent signals) within the wireless communication unit 200.

As regards the transmit chain 220, the input device 210 may be connectedto a modulator circuit 207, for instance via the signal processor 208.The input device 210 may generate a transmit signal and transmit thesignal to the modulator circuit 207. The transmit signal may beprocessed between generation and reception by the transmitter/modulationcircuit, and for example be subjected to an analog-to-digitalconversion, be converted into packets of data or other suitableprocessing by the signal processor 208. The transmitter/modulationcircuitry 207 and receiver front-end circuitry 203 comprise frequencyup-conversion and frequency down-conversion functions (not shown). Thetransmitter/modulation circuit 207 may modulate the transmit signal intoa modulated signal and pass the, envelope modulated, transmit signal toa power amplifier 10 to be radiated from the antenna 201. The modulatorcircuit 207 and the power amplifier 10 are operationally responsive tothe controller 205, with an output from the power amplifier 10 connectedto the duplex filter or antenna switch 202. As shown in FIG. 3, theoutput of the power amplifier 10 may be connected to an input of anenvelope detector 100. The -envelope detector 100 may be connected withthe output to a control input 101 of a bias source 100, which isconnected to a bias input of the power amplifier 10.

In the foregoing specification, the invention has been described withreference to specific examples of embodiments of the invention. It will,however, be evident that various modifications and changes may be madetherein without departing from the broader spirit and scope of theinvention as set forth in the appended claims. For example, thetransistors shown in FIG. 2, may be replace with a complementaryversion, with, for instance, the NPN HBT may be replaced with PNP HBTand vice versa. Also, transistors of a particular type may be replacewith a different type of transistors, for instance a HBT may be replacedby a MESFET or a PHEMT transistor. Also, resistors may be replaced withcapacitances and inductances. Also, the amplifier circuit can bedesigned in a different manner, for instance by adding extra amplifierstages, e.g. in the form of transistors. Furthermore, the connectionsbetween units in the envelope detector and/or the amplifier circuit maybe an type of connection suitable to transfer the signal between theunits or devices. The connections may for example be directionconnections or indirect connections.

Also, the invention is not limited to physical devices or unitsimplemented in non-programmable hardware but can also be applied inprogrammable devices or units able to perform the desired devicefunctions by operating in accordance with suitable program code.Furthermore, the devices may be physically distributed over a number ofapparatuses, while functionally operating as a single device. Forexample, the envelope detector may include two or more discretesemiconductor components. E.g. the sensor 102 and the filter 103 may beimplemented as separate integrated circuits.

Also, devices functionally forming separate devices may be integrated ina single physical device. For example, the amplifier circuit may forexample be implemented as a single monolithic integrated circuit, forexample manufactured using a RF Complementary Metal Oxide Silicon (RFCMOS), merged CMOS and bipolar (Bi-CMOS), a SiGe, or a GaAs process.However, the invention is not limited to an integrated circuit or aparticular topology or a specific device technology.

However, other modifications, variations and alternatives are alsopossible. The specifications and drawings are, accordingly, to beregarded in an illustrative rather than in a restrictive sense.

In the claims, any reference signs placed between parentheses shall notbe construed as limiting the claim. The word ‘comprising’ does notexclude the presence of other elements or steps then those listed in aclaim. Furthermore, the words ‘a’ and ‘an’ shall not be construed aslimited to ‘only one’, but instead are used to mean ‘at least one’, anddo not exclude a plurality. The mere fact that certain measures arerecited in mutually different claims does not indicate that acombination of these measures cannot be used to advantage.

1. An envelope detector for detecting a modulation envelope of amodulated signal, comprising: a sensor having a sensor input, forsensing a signal forming a measure for the amount of electrical powerpresented at said sensor input, which sensor input is electricallyconducting connectable to an electrical path, along which electricalpath said modulated signal is transmitted; a filter for removing fromthe sensed signal at least a part contributed to non-envelope signalcomponents in the modulated signal; and a detector output connected tosaid filter for outputting an envelope signal.
 2. An envelope detectoras claimed in claim 1, wherein said sensor is a current sensor forsensing the amount of current flowing through said electrical path andsaid sensed signal forms a measure for said amount of current.
 3. Anenvelope detector as claimed in claim 1, wherein the sensor includes anactive electrical device for generating an image signal which forms animage of said modulated signal, which active electrical device isconnected with a device input to said sensor input for sensing saidmodulated signal, and has a device output for outputting said imagesignal.
 4. An envelope detector as claimed in claim 3, including acurrent-to-voltage converter and wherein said active electrical deviceincludes a controllable current source which is connected with a currentinput to said sensor input and with a current output to saidcurrent-to-voltage converter.
 5. An envelope detector as claimed inclaim 3, wherein said sensor includes a sensor control input and whereinsaid active electrical device has an amplitude control input connectedto said sensor control input, for inputting an amplitude control signal,and said active electrical device is arranged to control at least theamplitude of said image signal based on said amplitude control signal.6. An envelope detector as claimed in claim 3, wherein said sensorincludes a sensor control input, wherein said active electrical devicehas a controllable bias and wherein said active electrical deviceincludes a bias input connected to said sensor control input forinputting a bias signal.
 7. An envelope detector as claimed in claim 1,further including a phase shifter for shifting the phase of saidenvelope signal relative to said modulated signal.
 8. An envelopedetector as claimed in claim 1, including an network r between saidsensor and a detector input, for reducing the swing of the signalinputted to said sensor.
 9. An envelope detector as claimed in claim 8,wherein said network includes an RC network with a time-constant whichis smaller than the inverse of the carrier frequency.
 10. An envelopedetector as claimed in claim 1, including a DC-Dc converter connected tosaid detector output for changing at least a DC level of said envelopesignal.
 11. A linearizer comprising an envelope detector as claimed inclaim
 1. 12. An electronic circuit, including: an electronic devicehaving an device input, and at least one device output and optionally atleast one preceding stage which, in a direction of signal processing, ispresent upstream of the electronic device; a feedback loop and/or a feedforward loop, said loop connecting a point in a signal path upstream ordownstream of said device input to said device input, said loopincluding: a linearizer as claimed in the preceding claim connected witha sensor input to said point in the signal path.
 13. An electroniccircuit as claimed in claim 12, wherein said electronic device is one ofthe group consisting of: amplifier, power amplifier, low noiseamplifier, mixer, frequency multiplier, frequency up converter,frequency down converter and the like.
 14. An electronic circuit asclaimed in claim 12, wherein said electronic device includes an outputstage and at least one preceding stage which, in a direction of signalprocessing, is present upstream of the output stage, and wherein saiddevice input is an input of the output stage or of a preceding stage.15. An electronic circuit as claimed in claim 12, further including abias source connected to said device input, said bias source having abias control input connected to said detector output, for controllingthe bias based on the envelope signal.
 16. A monolithic integratedcircuit including an electronic circuit as claimed in claim
 12. 17. Awireless communication unit, including: a signal generator forgenerating a signal; an electronic circuit as claimed in claim 12 forobtaining an amplified signal by amplifying said generated signal; andan antenna for transmitting said amplified signal.
 18. A method fordetecting a modulation envelope of a modulated signal, including:sensing a signal forming a measure for the amount of electrical powerpresented at said sensor input via an electrical conducting connectionto an electrical path, along which electrical path said modulated signalis transmitted; removing from the sensed signal at least a partcontributed to non-envelope signal components in the modulated signal;and outputting an envelope signal.
 19. An envelope detector as claimedin claim 2, wherein the sensor includes an active electrical device forgenerating an image signal which forms an image of said modulatedsignal, which active electrical device is connected with a device inputto said sensor input for sensing said modulated signal, and has a deviceoutput for outputting said image signal.
 20. An envelope detector asclaimed in claim 3, further including a phase shifter for shifting thephase of said envelope signal relative to said modulated signal.